Pallet replacing device

ABSTRACT

A pallet P held in a vertical position is moved from a pallet mounting surface, formed to extend vertically on a table  115  of a machine tool  101,  to a pallet mounting surface formed vertically on a pallet support member  17  of a pallet changer  11.  After rotationally indexing a swivel base  15  by 180 degrees about a vertical axis, a pallet P′ is moved from the pallet support member  17  to the table  115.

TECHNICAL FIELD

The present invention relates to a pallet changer for changing a palletheld in a vertical position on a vertical surface, of a table or apallet mount of a machine tool, on which the pallet is removablymounted.

BACKGROUND ART

A machine tool in which a pallet having a workpiece fixed thereon ismounted removably on the table or the pallet mount of a machine tool tomachine the workpiece is widely used. In such a machine tool, a palletchanger is used to replace a machined workpiece with a workpiece yet tobe machined. In the conventional pallet changer, new and old pallets areplaced on arms extending in opposite horizontal directions on both sidesof a rotary shaft extending vertically, and the pallets are replaced byrotating the rotary shaft by 180 degrees and thus exchanging thepositions of the new and old pallets.

The pallet changer described above is configured to support the palletsin a horizontal position. However, a pallet changer supporting thepallets in a vertical position is also available.

International Publication WO01/94071, for example, discloses a palletmount arranged to face the forward end of a spindle and adapted to berotatable about a horizontal axis. This pallet mount includes two palletmounting surfaces back-to-back and, by rotating the pallet mount by 180degrees about a horizontal axis, new and old pallets can be exchanged.

U.S. Pat. No. 5,172,464 discloses a pallet magazine in which a pluralityof pallet holders are disposed, adjacent to a machine tool, radially andat equal angular intervals about a rotary shaft extending in horizontaldirection, and a pallet for fixing a workpiece thereon is mounted oneach pallet holder. One of the pallets supported vertically in thispallet magazine is exchanged with a pallet mounted on a vertical tableof the machine tool.

However, International Publication WO01/94071 and U.S. Pat. No.5,172,464 do not disclose a pallet changer in which pallets are mountedin a vertical position on the two side surfaces of a pallet-supportingmember rotatable about a vertical axis.

DISCLOSURE OF THE INVENTION

The conventional pallet changer for holding the pallets in a horizontalposition on arms rotatable about a vertical axis or the pallet changersdisclosed in International Publication WO01/94071 and U.S. Pat. No.5,172,464 pose a problem that the pallet for a large tabular workpieceis large and a large area is required to exchange the pallet, resultingin a large floor space required to install a pallet changer.

The technical subject of the present invention is to solve theabove-mentioned problem of the prior art, and the object thereof is toreduce the floor space of a pallet changer for changing a pallet onwhich a large tabular workpiece can be mounted.

In order to achieve this object, according to the present invention,there is provided a pallet changer for changing a pallet of a machinetool, which machine tool includes a spindle supported so as to berotatable about a horizontal axis for mounting a tool at the forward endthereof, and a table or a pallet mount facing the front of the spindlefor mounting a pallet on a vertical surface perpendicular to the axis ofthe spindle, and which machine tool machines a workpiece fixed on thepallet with the tool by moving the tool and the table relative to eachother. The pallet changer is characterized by including a pallet supportmember disposed adjacent to the table or the pallet mount and adapted tobe able to be rotationally indexed about a vertical axis, said palletsupport member having at least two vertical pallet mounting surfaces oneach of which the pallet can be removably mounted; and a pallet movingmeans for moving and transferring the pallet in a vertical positionbetween the table or the pallet mount and the pallet support member.

The pallet in a vertical position is moved and transferred between thetable or the pallet mount and the pallet support member, and the palletsupport member is rotated about the vertical axis so that a new palletis indexed at the pallet change position. Thus, the new pallet in avertical position is moved to the table or the pallet mount where it istransferred. As the pallets are moved and rotated in a verticalposition, the floor space required for the pallet change operation isreduced.

Also, there is provided a pallet changer wherein the pallet supportmember is arranged as an extension of the table or the pallet mount inthe horizontal direction perpendicular to the spindle axis and whereinthe pallet mounting surface on the side of the pallet support memberwhere the pallet moves is arranged in parallel to the pallet mountingsurface of the table or the pallet mount.

The pallet support member is arranged at a position in the extension ofthe table in the horizontal direction perpendicular to the spindle axis,and therefore the pallet moves only linearly. This configuration alsomakes it possible to reduce the floor space required for the palletchange operation.

According to the present invention, the pallets are moved and replacedin a vertical position between the pallet mounting surface formed toextend vertically on the table or the pallet mount of a machine tool andthe pallet mounting surface formed to extend vertically on the palletchanger. Therefore, the installation space for the pallet changer can beremarkably reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a pallet changer according to apreferred embodiment of the present invention together with a machinetool;

FIG. 2 is a perspective view of the table of the machine tool shown inFIG. 1;

FIG. 3 is a perspective view of a pallet;

FIG. 4 is a sectional view showing the pallet clamped on the table;

FIG. 5 is a sectional view showing the pallet unclamped from the table;

FIG. 6 is a plan view of the pallet changer;

FIG. 7 is a perspective view showing the pallet changer together withthe machine tool for explaining the pallet change operation;

FIG. 8 is another perspective view showing the pallet changer togetherwith the machine tool for explaining the pallet change operation; and

FIG. 9 is another perspective view showing the pallet changer togetherwith the machine tool for explaining the pallet change operation.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

First, referring to FIG. 1, a pallet changer 11 according to a preferredembodiment of the present invention is arranged adjacent to a machinetool 101 to exchange new and old pallets P and P′ while they are kept ina vertical position. The machine tool 101 includes, as main components,first and second beds 103 a, 103 b, a column 107 disposed on the firstbed 103 a, a spindle head 109 disposed on the column 107 for rotatablysupporting a spindle (not shown), and a table 115 disposed on the secondbed 103 b.

Z-axis guide rails 105 a, 105 b are disposed on the upper surface of thefirst bed 103 a to extend in parallel to a rotational axis O of thespindle. The column 107 is adapted to move reciprocably along the Z-axisguide rails 105 a, 105 b. Also, the machine tool 101 has, as a Z-axisfeed means, a threaded shaft (not shown) extending along Z-axis in thefirst bed 103 a, a servo motor (not shown) connected to one end of thethreaded shaft and a nut (not shown) disposed at the lower end of thecolumn 107 so as to be engaged with the threaded shaft.

The spindle is supported by the spindle head 109 so as to be rotatableabout the horizontal rotational axis O and to be projected in the Z-axisdirection from the front surface of the column 107. A tool T is mountedon the forward end of the spindle through a well-known tool mountingmeans such as a tool holder (not shown) and a draw bar (not shown). Apair of parallel Y-axis guide rails disposed on the front surface (notshown) of the column 107 to extend vertically (along Y-axis direction).The spindle head 109 is mounted on the column 107 so as to movereciprocably along the Y-axis guide rails. Also, the machine tool 101includes, as a Y-axis feed means, a threaded shaft (not shown) disposedin the column 107 to extend in the Y-axis direction, a servo motor 111connected to one end of the threaded shaft, and a nut (not shown)disposed on the spindle head 109 so as to be engaged with the threadedshaft.

In this embodiment, the second bed 103 b makes up a member separate fromthe first bed 103 a, and is arranged in spaced relation with the firstbed 103 a in front of the latter, i.e. near the forward end of thespindle. A pair of X-axis guide rails 113 a, 113 b are disposed on theupper surface of the second bed 103 b to extend in parallel to eachother along X-axis perpendicular to Y- and Z-axes. The table 115 isadapted to move reciprocably along the X-axis guide rails 113 a, 113 b.The machine tool 101 also includes, as an X-axis feed means, a threadedshaft (not shown) disposed in the second bed 103 b to extend in theX-axis direction, a servo motor (not shown) connected to one end of thethreaded shaft, and a nut (not shown) disposed on the table 115 so as tobe engaged with the threaded shaft. In this way, the machine tool 101machines a workpiece (not shown) on the pallet P mounted on the table115 while moving the workpiece and the tool T relatively to each otherin the directions along three orthogonal axes by the X-, Y- and Z-axisfeed means.

Next, with reference to FIGS. 2 to 4, the configuration of the table 115and the pallet P (P′) will be explained. The pallets P and P′ have thesame configuration, and therefore only the pallet P will be describedbelow.

In FIG. 2, the table 115 is formed of a member which has a substantiallytriangular cross section as a whole and which is provided with a platemember 117 having a vertical pallet mounting surface 117 a facing theforward end of the spindle. The pallet mounting surface 117 a hasdisposed thereon a lift means 119 for vertically moving the pallet Palong the pallet mounting surface 117 a, a guide means for guiding thepallet P in the X-axis direction along the pallet mounting surface 117a, a support means for supporting the pallet P in Y- and Z-axisdirections on the pallet mounting surface 117 a, and a clamp means forfixing the pallet P on the pallet mounting surface 117 a. Further, thepallet mounting surface 117 a has disposed thereon an engagingprotrusion 148 making up an X-axis positioning means for positioning thepallet P along X-axis on the pallet mounting surface 117 a.

The lift means 119 includes a plurality of brackets 121 spaced apartfrom each other in the X-axis direction along the pallet mountingsurface 117 a, a plurality of link members 123 adapted to be rotatableabout the rotary shafts 125 mounted on the brackets 121 and extending inthe Z-axis direction, a plurality of lift rollers 127 each mounted atthe upper end of each link member 123 so as to be rotatable about therotary shaft extending in the Z-axis direction, a connecting member 129connected to the lower ends of the link members 123 and extending in theX-axis direction, and a lift cylinder 131 constituted by a fluidcylinder or preferably a pneumatic cylinder having a piston rod 131 aconnected to the connecting member 129 to be movable in the X-axisdirection. In the lift means 119, this configuration allows each liftroller 127 to be moved vertically, depending on the position of thepiston rod 131 a, between a lift position shown in FIG. 2 and a supportposition where the link member 123 is rotated counterclockwise by apredetermined angle from the position shown in FIG. 2. The lift rollers127 make up a part of the lift means 119 and a part of the guide meansdescribed later.

The guide means, in addition to the lift rollers 127, includes firsthorizontal guide rollers 137 a and second horizontal guide rollers 140,147. The first guide rollers 137 a are supported on a plurality ofmovable clamp members 137 disposed along the upper and lower edges ofthe pallet mounting surface 117 a and spaced apart from each other inthe X-axis direction so as to be rotatable about rotary shafts extendingin the Y-axis direction. The second horizontal guide rollers 140, 147are supported on a plurality of brackets 138 disposed below the uppermovable clamp members 137 along the pallet mount surface 117 a andspaced apart from each other in the X-axis direction on one hand and ona plurality of brackets 145 disposed above the lower movable clampmembers 137 along the pallet mounting surface 117 a and spaced apartfrom each other in the X-axis direction on the other hand, so as to berotatable about rotary shafts extending in the Y-axis direction. Themovable clamp members 137 make up a part of the guide means and anessential part of the clamp means described later.

The support means includes a plurality of first and second horizontalsupport members 133, 139 mounted on the pallet mounting surface 117 aand a plurality of vertical support members 149. The first horizontalsupport members 133 are arranged along the upper and lower edges of thepallet mounting surface 117 a and are spaced apart from each other inthe X-axis direction, while the second horizontal support member 139 arearranged substantially along the center line of the pallet mountingsurface 117 a and are spaced apart from each other in the X-axisdirection. The first and second horizontal support members 133, 139 havefirst and second horizontal support surfaces 135, 141, respectively,formed to extend vertically in opposed relation to the pallet P mountedon the pallet mounting surface 117 a. The vertical support members 149are arranged below the second horizontal support members 139, are spacedapart from each other in the X-axis direction and each has a verticalsupport surface 151 facing upward and formed to extend horizontally.

The clamp means includes a movable clamp member 137, an unclamp cylinder(not shown) constituted by a fluid cylinder, preferably a pneumaticcylinder (not shown), for separating the movable clamp member 137 in theZ-axis direction from the pallet mounting surface 117 a, a clamp spring133 a (FIGS. 4, 5) serving as an urging means for urging the movableclamp member 137 toward the pallet mounting surface 117 a, and astationary clamp member 143 fixed on the horizontal support member 139.In this embodiment, the unclamp cylinder is built into the first supportmember 133.

In the case where the pallets P, P′ and the workpiece are relativelylight in weight, the pallets may be supported directly on the liftrollers 127 serving as the guide means without any lift means and anyvertical support means.

Next, referring to FIG. 3, the pallet P includes a plate member 201having a workpiece mounting surface 201 a for mounting a workpiece (notshown) thereon. When the pallet P is mounted on the pallet mountingsurface 117 a, the workpiece mounting surface 201 a forms a verticalsurface opposed to the forward end of the spindle. The surface of theplate member 201 opposite to the workpiece mounting surface 117 athereof constitutes a table surface 201 b facing the pallet mountingsurface 117 a of the table 115. The table surface 201 b has disposedthereon a guide means for guiding the pallet P along the pallet mountingsurface 117 a in cooperation with the guide means of the table 115 and abearing means in contact with the support means. The table surface 201 bhas further arranged thereon a fitting portion 221 serving as apositioning means adapted to engage the engaging protrusion 148 of thetable 115 for positioning the pallet P in the X-axis direction on thepallet mounting surface 117 a.

The guide means of the pallet P includes a pair of first guide rails 207a, 207 b extending in parallel with each other along the upper and loweredges of the table surface 201 b, and a pair of second guide rails 205a, 205 b extending in parallel with the first guide rails 207 a, 207 b,respectively. Each of the first guide rails 207 a, 207 b has a firstguide surface 206 adapted to contact the first horizontal guide roller137 a when the pallet P is mounted on the pallet mounting surface 117(see FIGS. 4 and 5). Each of the second guide rails 205 a, 205 b has asecond guide surface 204 adapted to contact the second horizontal guiderollers 140, 147 when the pallet P is mounted on the pallet mountingsurface 117. Referring to FIGS. 3 to 5, it will be understood that thefirst and second guide surfaces 206, 204 are formed to face in oppositedirections along the Z-axis. When the lift means 119 is in the liftposition shown in FIG. 2, the lift rollers 127 are each in contact withthe lower end surface of the second guide rail 205 a, of the first andsecond guide rails 205 a, 205 b, arranged on the upper side when thepallet P is mounted on the pallet mounting surface 117 (see FIG. 5).

The bearing means includes a plurality of first horizontal bearingmembers 209, a plurality of second horizontal bearing members 213 and aplurality of vertical bearing members 217, which are mounted on thetable surface 201 b of the pallet P. The first horizontal bearingmembers 209 are disposed on both sides of the first guide rails 207 a,207 b and spaced apart from each other in the X-axis direction, and eachof them has a first horizontal bearing surface 211 adapted to contactthe first horizontal support surface 135 of the first horizontal supportmember 133 when the pallet P is mounted on the pallet mounting surface117 (see FIGS. 4 and 5). The second horizontal bearing members 213 aredisposed on both sides of substantially the center line of the pallet Pin the X-axis direction and spaced apart from each other in the X-axisdirection, and each of them has a second horizontal bearing surface 213adapted to contact the second vertical support surface 141 of the secondhorizontal support member 139 when the pallet P is mounted on the palletmounting surface 117 (see FIGS. 4 and 5). The vertical bearing members217 are disposed in the vicinity of the second horizontal supportmembers 139 and each of them has a vertical bearing surface 219 adaptedto contact the vertical support surface 151 of the vertical supportmember 149. Each first horizontal bearing member 209 is also held orclamped between the movable clamp member 137 and the first horizontalsupport member 133 (see FIG. 5).

The embodiment having the pallet mounting surface 117 a perpendicular tothe table 115 has been described above. However, as an alternative, apallet mount having a vertical pallet mounting surface may be fixedlyerected on the horizontal upper surface of the table, and variousmembers for mounting and demounting the pallet described in FIG. 2 maybe arranged on the pallet mount.

Next, referring to FIGS. 1 and 6, the pallet changer 11 includes, asmain components, a bed 13 making up a base, a swivel base 15 disposed onthe bed 13 so as to be rotatable about the vertical axis, and a palletsupport member 17 formed of a tabular member erected on the swivel base15 for removably mounting one pallet on each side surface thereof. Theside surfaces of the pallet support member 17 constitute pallet mountingsurfaces 17 a, 17 b. The pallet mounting surfaces 17 a, 17 b havedisposed thereon such devices as a lift means 119, a guide means, asupport means, a positioning means and a clamp means of the table 115,which are illustrated by reference numerals 19, 21 in FIG. 1. Also, inFIG. 1, the pallet support member 17 has mounted thereon a new pallet P′carrying a workpiece yet to be machined (not shown), and the table 115has mounted thereon an old pallet P carrying a workpiece in process (notshown) or a workpiece already machined (not shown).

The pallet changer 11 further includes a pallet moving means for movingand transferring the pallets P, P′ between the pallet support member 17and the table 115. Referring to FIG. 6, the pallet moving means includesa tabular movable base member 23 disposed at the top of the palletsupport member 17 and a chain drive means disposed on the movable basemember 23 and adapted to move together with the movable base member 23.The movable base member 23 is movable in the X- and Z-axis directions onthe pallet support member 17 by a base drive mechanism not shown. Thechain drive means includes a drive motor 25 having an output shaft 25 aextending in the Y-axis direction, a driving sprocket 27 mounted on theoutput shaft 25 a of the drive motor 25, a driven sprocket 29 mounted onthe rotary shaft 29 a extending in parallel to the output shaft 25 a ofthe drive motor 25, a drive chain 31 extending between the drivingsprocket 27 and the driven sprocket 29, a first sprocket 33 mounted onthe rotary shaft 29 a concentrically with the driven sprocket 29, asecond sprocket 35 mounted on a rotary shaft 35 a disposed on theopposite side of the output shaft 25 a of the drive motor 25 andextending in the Y-axis direction, a driven chain 37 extending betweenthe first and second sprockets 33, 35 and adapted to move around thefirst and second sprockets 33, 35 in the X-Z plane, and an engagingportion 39 mounted on the driven chain 37 and adapted to engage with theengaging portion 203 of the pallets P, P′.

Referring to FIGS. 7 to 9, the operation of this embodiment will beexplained below. In the following description, the pallet-changingprocess is executed from the state in which the workpiece (not shown)fixed on the pallet P mounted on the table 115 has been completelymachined (FIG. 1).

Once the workpiece is completely machined in FIG. 1, the machine tool101 starts the pallet change operation. Specifically, first, the X-axisfeed means is activated, so that the table 115 moves along the X-axisguide rails 113 a, 113 b toward the pallet change position where thepallets P, P′ are exchanged between the table 115 and the pallet changer11, i.e. the X-axis stroke end where the table 115 is positioned nearestto the pallet changer 11. Then, the table 115 is set in position. Whenthe table 115 arrives at the pallet change position, the pallet unclampoperation described later is started.

Specifically, in FIGS. 2 and 5, an unclamp cylinder (not shown) issupplied with a working fluid, so that the movable clamp member 137moves toward the pallet P in the X-axis direction against the urgingforce of the clamp spring 113 a. As a result, the first and secondhorizontal bearing members 209, 213 thus far held between the movableclamp member 137 and the first horizontal support member 133 and betweenthe stationary clamp member 143 and the second horizontal support member139 can now be moved freely. When the movable clamp member 137 furtheradvances and comes into contact with the pallet P, the pallet P is urgedin a direction (rightward in FIG. 5) away from the table 115 by themovable clamp member 137.

As soon as or after the movable clamp member 137 begins to move, theworking fluid is supplied to the lift cylinder 131 so that the pistonrod 131 a extends. As a result, the connecting member 129 moves leftwardin FIG. 2, and the link member 123 rotates clockwise from the supportposition to the lift position shown in FIG. 2. Then, the lift rollers127 of the lift means 119 come into contact with the lower end surfaceof the upper guide rail 205 a of the second guide rail pair, so that thepallet 117 moves up and is held in a vertical position by the liftrollers 127. In this way, the vertical bearing surfaces 219 of thevertical bearing members 217 move away from the vertical supportsurfaces 151 of the vertical support members 149, so that the pallet Pbecomes movable in the horizontal direction.

The pallet P, after becoming movable in the horizontal direction, isurged by the movable clamp members 137 away from the pallet mountingsurface 117 a of the table 115, and the fitting portion 221 moves awayfrom the engaging protrusion 148, thereby disengaging them from eachother. Also, as the result of the pallet P being urged by the movableclamp members 137, the first horizontal guide rollers 137 a are pressedagainst the first guide surfaces 206, while at the same time the secondhorizontal guide rollers 140, 147 are pressed against the second guidesurfaces 204. In this way, the pallet P is subjected to the samemagnitude of pressure in opposite directions between the firsthorizontal guide rollers 137 a and the first guide rails 207 a, 207 band between the second horizontal guide rollers 140, 147 and the secondguide rails 207 a, 207 b, with the result that the pallet P can be heldso as to be movable in the X-axis direction but immovable in the Z-axisdirection.

As soon as or after the pallet change operation of the machine tool 101is started, a pallet change command is sent out from a machine controlunit to the pallet changer 11. Upon receipt of the pallet changecommand, the pallet changer 11 rotates the swivel base 15 to positionthe pallet support member 17 so that one pallet mounting surface 17 a ofthe pallet mounting surfaces 17 a, 17 b thereof having no pallet P or P′mounted thereon becomes parallel to the pallet mounting surface 117 a ofthe table 115, i.e. the pallet mounting surface 17 a is laid in the X-Yplane (see FIG. 6).

Next, the movable base member 23 begins to move toward the table 115 inthe X-axis direction. When the engaging member 39 arrives at a positionwhere it can engage with the engaging portion 203 of the old pallet Pmounted on the table 115, the movable base member 23 comes to stop andmoves toward the old pallet in the Z-axis, so that the engaging member39 comes to engage the engaging recess 203 a of the engaging portion203. Then, the movable base member 23 is retreated in the X-axisdirection, while at the same time the drive motor 25 rotates clockwisein FIG. 6. As a result, the driven chain 37 is rotated in the directionof arrow R, so that the old pallet P is pulled from the pallet mountingsurface 117 a of the table 115 (see FIG. 7) and moves to the palletmounting surface 17 a of the pallet support member 17. As alreadydescribed, the pallet mounting surface 17 a has a similar configurationto the pallet mounting surface 117 a of the table 115, and the pallet Pthat has moved onto the pallet mounting surface 17 a of the palletsupport member 17 is guided to and fixed at a predetermined position onthe pallet mounting surface 17 a by the clamp operation similar to thatof the table 115 as described later. When the pallet P is fixed on thepallet mounting surface 17 a, the movable base member 23 moves away fromthe pallet P in the Z-axis direction, to thereby disengage the engagingmember 39 and the engaging member 203 from each other.

Then, the swivel base 15 rotates (see FIG. 8), and the pallet supportmember 17 is positioned such that the pallet mounting surface 17 bhaving the new pallet P′ mounted thereon is arranged in the X-Y plane(see FIG. 9). Next, the new pallet P′ mounted on the pallet mountingsurface 17 b of the pallet support member 17 is unclamped by the sameunclamp operation as that of the table 115 described above, and themovable base member 23 begins to move toward the table 115 in the X-axisdirection. As soon as or after the movable base member 23 begins tomove, the drive motor 27 rotates counterclockwise in FIG. 6, and thedriven chain 37 rotates in the direction opposite to the arrow R. As aresult, the new pallet P′ begins to move in the opposite direction alongthe moving path of the old pallet P from the pallet mounting surface 117a of the table 115 toward the pallet mounting surface 17 a of the palletsupport member 17.

In this way, the new pallet P′ moves from the pallet mounting surface 17b of the pallet support member 17 to the pallet mounting surface 117 aof the table 115. In the process, the first horizontal guide roller 137a comes into contact with the first guide surface 206, and the secondhorizontal guide rollers 140, 147 come into contact with the secondguide surfaces 204. At the same time, the lift rollers 127 come intocontact with the lower end surface of the upper guide rail 205 a of thesecond guide rail pair. As the result of each guide rail coming intocontact with the rollers, the new pallet P′ is guided in the X-axisdirection along the pallet mounting surface 117 a (see FIG. 5).

When the movable base member 23 arrives at a predetermined position inthe X-axis direction and the drive motor 25 rotates by a predeterminedangle so that the new pallet P′ arrives at a position where the fittingportion 221 serving as an X-direction positioning means can engage theengaging protrusion 148, the movable base member 23 moves away from thenew pallet P′ in the Z-axis direction and returns onto the palletsupport member 17 of the pallet changer 11. At the same time, the table115 starts the clamp operation. Specifically, the working fluid stopsbeing supplied to the lift cylinder 131, and the piston rod 131 a isretreated, with the result that the link members 123 rotatecounterclockwise about the rotary shaft 125 from the lift position shownin FIG. 2 to the support position, so that the lift rollers 127 movedown with the new pallet P′. When the vertical bearing surfaces 219 ofthe vertical bearing members 217 come into contact with the verticalsupport surfaces 151 of the vertical support members 149, the liftrollers 127 come away from the lower end surface of the first guide rail205 a, so that the new pallet P′ is supported vertically by the verticalsupport members 149 and accurately positioned in the Y-axis direction.

Then, the pressure fluid is not supplied to the unclamp cylinder (notshown), and the movable clamp members 137 move toward the palletmounting surface 117 a of the table 115 in the Z-axis direction as theresult of the pressure fluid being supplied to the clamp cylinder (notshown). Thus, the first horizontal bearing members 209 are pressed bythe movable clamp members 137, and the fitting portion 221 and theengaging protrusion 148 engage each other. The pallet P′ is thusaccurately positioned in the X-axis direction. At the same time, thefirst horizontal bearing members 209 are clamped between the firsthorizontal support members 133 and the movable clamp members 137, whileeach of second horizontal bearing members 213 is clamped between thesecond horizontal support member 139 and the stationary clamp member143. Thus, the new pallet P′ is supported horizontally by the first andsecond horizontal support members 133, 139, while at the same time beingaccurately positioned in the Z-axis direction. The clamp springs 133 aare provided for preventing the pallet P′ from being released from thetable 115 in case of a power failure or an emergency stop.

As long as or after the new pallet P′ is clamped to the table 115, thepallet support member 17 rotates 180 degrees and moves the old pallet Pto the position designated by P′ in FIG. 6 in preparation for theoperation of replacing the machined workpiece mounted on the old palletP with the workpiece yet to be machined. At this position, the operatorcan perform the mounting and demounting operation, of the workpiece, onthe old pallet P.

1. A pallet changer for changing a pallet of a machine tool, saidmachine tool comprising a spindle supported so as to be rotatable abouta horizontal axis for mounting a tool at the forward end thereof, and atable or a pallet mount facing the front of said spindle for mounting apallet on a vertical surface perpendicular to the axis of said spindle,said machine tool machining a workpiece fixed on said pallet with saidtool by moving said tool and said table relative to each other, saidpallet changer characterized by comprising: a pallet support memberdisposed adjacent to said table or said pallet mount and adapted to berotationally indexed about a vertical axis, said pallet support memberhaving at least two vertical pallet mounting surfaces on each of whichsaid pallet can be removably mounted; and a pallet moving means formoving and transferring said pallet in a vertical position between saidtable or said pallet mount and said pallet support member.
 2. The palletchanger according to claim 1, wherein said pallet support member isarranged in the extension of said table or said pallet mount in thehorizontal direction perpendicular to the spindle axis, and wherein saidpallet mounting surface, on the side of said pallet support member wheresaid pallet moves, is arranged in parallel to said pallet mountingsurface of said table or said pallet mount.